Not Applicable.
1. Field of the Invention
The invention relates generally to the area of manufacturing electrically conductive, complex, porous structures which are optionally metallised or metallic.
The invention relates more particularly to the area of manufacturing complex structures of high porosity which are optionally metallised or metallic for use as electrodes for the electrolysis of liquid effluents, to detect and trap organic or biological molecules, as support electrodes for storage cells, catalysis supports, filtering media, sound insulators, electromagnetic, nuclear and antistatic structures, heat exchangers, etc.
The metallic or metallised structures according to the invention are of the foam, nonwoven or woven type with a high degree of open porosity, giving the impression of a dense network of fibres or meshes with a three-dimensional skeleton, defining a large number of voids which are interconnected with each other and with the exterior of the structures.
The foam structures consist of a cross-linked honeycomb structure with a high porosity (greater than 80% and able to reach about 98%) and with a porosity which has been opened up by expansion, in which the mesh in the network is interconnected in its entirety or at least to a very large extent.
The nonwovens are random tangles of non-woven fibres (however, the bulk of them are located substantially in the plane of the xe2x80x9cnapxe2x80x9d which is formed), defining enclosed, interconnected, inter-fibre spaces with varying shapes and sizes. The fibres therein may be pasted over with a bonding agent, or not.
The woven fabrics are structures formed by assembling interlaced, woven or meshed textiles from threads or fibres. They can be provided in the form of thick and complex structures, in particular when they are two external woven faces linked by knitted loops of thread which keep them apart but also interconnected, such as are produced, for example, by Raschel type weaving looms.
These various complex porous structures which, according to the invention, may be intended to be metallised throughout their entire thickness, on all the available surface area, without clogging the pores, can be supplied in various basic materials.
The foams are organic, mineral or synthetic materials and in particular polymers such as polyamide, polyurethane (polyesters or polyethers) or polypropylene.
The nonwoven and woven materials are also organic, mineral or synthetic materials, such as those mentioned above, or glass, rock wool or carbon fibres, or natural fibres such as cotton, wool or the like.
2. Description of the Prior Art
A variety of methods for metallising such structures have been suggested, among which are:
chemical deposition of metal, followed by one or more electrochemical coatings,
deposition of particles of carbon or graphite, in particular in the form of a conductive paint or lacquer, followed by one or more electrochemical coatings,
metallic deposition under vacuum, in particular by cathodic evaporation, gaseous diffusion or ionic deposition, followed by one or more electrochemical coatings,
deposition by thermal decomposition of a metallic compound in the vapour phase,
chemical deposition of a conductive polymer, followed by one or more electrochemical coatings of metal.
In all cases where it is intended to proceed to one or more electrochemical coatings, it is best first to sensitise, that is to make electrically conductive, the surface which is to be metallised using an electrochemical route. This is the function of the xe2x80x9cconductive activationxe2x80x9d stage which appears in most of the procedures cited (chemical deposition of metal or of polymers, deposition of particles of carbon, deposition under vacuum).
According to the procedures also described above for producing one or more electrochemical coatings, the activation processes (and this is one of their major limitations) enable the complex porous structures which are subsequently to be metallised to be made conductive only in the form of sheets (or strips) of reduced thickness, which have to be transported and reeled through one or more treatment tanks (chemical baths, carbon lacquer baths, enclosures for deposition under vacuum).
Chemical deposition of metals and conductive polymers, and the deposition of particles of carbon or graphite have thus to be performed in sequence when working on an industrial scale, by unwinding the rolls of strips of foam, nonwoven or woven material, passing the material through a succession of treatment baths and then rewinding the material at the end of the activation line.
In a similar way, activation by deposition of metal under vacuum using the technique of cathodic evaporation is performed in the unrolled state, by passing in front of magnetrons, in a semi-continuous manner, between an input roll and an output roll.
Thus, the products which are activated are always present in a thin layer (sheets or strips). These thin layers are restricted to a thickness of the order of a millimeter or a few millimeters, depending on the porosity of the treated product, the dimensions of the pores or interstices and the power of penetration of the activation process.
Foams with the quality designated xe2x80x9c100 pplxe2x80x9d (100 pores per linear inch), that is with about 40 pores per linear centimeter at the surface can be activated on an industrial scale and in a satisfactory manner only with thicknesses of about 5 millimeters when using chemical deposition and under vacuum, and with thicknesses of less than about 3 millimeters when using carbon or graphite powder deposition.